Electric furnace



Jan. 24, 1933. 5. 1.. SIMPSON ELECTRIC FURNACE Filed D80. 12, 1931 .4. x mm Patented Jan. 24, 1933 GEORGE L.

rATEN orrlcr.

RESEARCH CORPORATION, OF PITTSBURGH, PENNSYLVANIA ELECTRIC FURNACE Application filed December a, 1931. Serial in. 580,690.

electric furnaces and more particularly to heat treating furnaces of the kind used for annealing purposes, although not necessarily restricted to this use.

In the heat treatment of metal sheets and other articles, great difiiculty has been experienced in obtainin uniform distribution of temperature throug out the charge. One attempted solution of this problem was to install heater elements in the hearth of the furnace, but this method of heating Was-found to be unsuccessful particularly in the treatmentof such articles as metal sheets du to the fact that very little heat energy is transmitted across the flat sides of the sheets because of the heat insulating layer of air or gases that separates each sheet from the sheet above it. There is still a strong tendency, therefore, for the upper portion of the charge to be heated to a. higher temperature than the lower portion-0f the charge.

An important object of my invention, therefore, is to provide a furnace in which a uniform temperature distribution throughout the charge will be obtained.

Other objects and advantages of my invention will be apparent during the course of the following description.

In the accompanying drawing, which forms a part ofthis specification, and wherein like characters of reference denote like parts throughout the same,

Figure 1 is a vertical sectional view through a furnace embodying my invention,

Figure 2 is a fragmentary elevation of a portion of the furnace wall showing one posinFigur sible arrangement of the resistor element,

and,

Figure 3 is a fragmentary'sectional view of a portion of the hearth and charge.

In the drawing wherein for the purpose of illustration is shown a preferred embodiment of my invention, the numeral 10 desi ates a furnace base having a hearth 11. furnace hood 12 has a removable roof 13 and is adapted to be placed over the base 10, as seen e 1. The hearth 11 extends up into the interior of the hood 12 for a substantial distance and supports the charge 14.

charge. If desired, the plate may The heating element is carried by the furnace hood or by its roof and comprises any suitable form of resistance element. For the purposes of illustration I have shown a resistance ribbon 15 supported in spaced loops by suitable spools 16 secured to the walls of the hood 12, but it is to be understood that other forms of resistors may be used, and other means of support utilized. The spools 16 are arranged in two rows, and the lower row ofsupporting spools is arranged a substantial distance below the top of the hearth 11, as seen in Figure 1. The broken line 17 in Figure 2 represents the hearth level.

It will be seen therefore, that the resistance heating elements 15 extend to a point below the top of the hearth which is the lower level of the charge. With this arrangement not only isthe lower portion of the charge heated directly from the resistance elements, but the upper portion of the hearth is also heated, and the tendency of the lower portion of the charge to run colder than-its upper portion, is counteracted.

It will also be noted that the distribution of the heat from the resistor may be regulated by changing the vertical location of the top row of supporting spools 16. By lowering the upper row of spools below the top of the charge, less heat will be directed onto the upper portion of the charge, and by raising the upper row of spools more heat is directed onto the upper portion of the charge. The lower row of spools should always be arranged below the top of the hearth for the best results, however,

In Figure 3 I have shown a metallic plate SIMIPSON, COBA OPOLIS, PENNSYLVANIA, ASSIGNOB '10 PITTSBURGH 17 of any suitable construction arranged on the hearth 11 and adapted to suppofrt ths 8 orme with transverse ribs 18. The plate 17 still further contributes to the effective heating of the lower portion of the charge. 7

The hearth 11 is provided with sloping sides as seen in Figure 1, which slope upwardly away from the heater elements 15 so as not to hamper greatly the free radiation of heat, from that portion of the heater element which is below the hearth level, to the charge. Were the hearth sides straight the lower ends of the heater elements would be used with my arrangement of heater elements,.I prefer to form the hearth as shown in Figured, in which the sides of the hearth are formed of firebrick shapes joined at their upper ends by a row of firebricks 19 arranged on end and forming the greater portion of the top of the hearth. The hearth is built on a heat insulating layer 20 which is also extended up between the side shapes to form, a central core 21 which supports the firebricks 19.

This construction provides a hearth built of mechanicallf strong refractories backed up by a heat insu atin layer. A solid fiat surface for the'top o the hearth is produced which is mechanically strong and not liable to warpage or displacement and at the same time provides adequate heat insulation. This feature is particularly valuable inthe annealing of sheets, because if the hearth should tend to warp or sag, bends or kinks in the sheets would result.

The charge 14' or charge plate 17 is largely supported by thefirebricks 19 in compression. Were the entire hearth area built up of fireb rick on end extending down to the first layer of heat insulating bricks, however,

a greater heat loss would be present than in the construction shown in Figure 1.

Suitable strips of asbestos 22 areiarranged overthe metal atthe bottom of the hood and hearth to reduce overheating and consequentlwgvarlp'age of the steel parts of the hearth and While I have shown and described the preferred embodiment of my invention, it is to be understood that various changes in the size, shape and arrangement of parts may be resorted to without departing from the spirit of my invention or the scope of the subjomed claims.

Having thus described my invention, what I claim and desire to protect by Letters Patent is:

1. An electric furnace comprising a heating hood, a hearth extending a substantial distance into said hood and adapted to receive the furnace charge, and a resistance element arranged in the hood and extending from a point spaced a substantial distance above the upper level of the hearth to a point spaced a substantial distance below th upper level of the hearth. V 2. An electric heating furnace comprising a furnace hood, a hearth extending a substantial distance into said hood and adapted,

to receive the furnace charge, a row of ribbon supports arranged on" the inner walls of the hood and spaced a substantial distance above the upper level of the hearth, a row of ribbon supports arranged on the inner walls of the furnace below the upper level of the hearth, and a resistance ribbon looped over said supports.

3. An electric heating furnace comprising a furnace hood, a hearth extending into said hood, a metallic charge supporting plate on said hearth, and a resistance element arranged in said hood and extending from a point above the upper level of said hearth to a pointvbelow the upper level of said hearth.

4. An electric heating furnace comprising a furnace hood, a hearth extending into said hood for a substantial distance, a ribbed metallic chargesupporting plate on said hearth, and a resistance element arranged in said hood and extending from a point spaced a substantial distance above the upper level of said hearth to a point spaced a substantial distance I below the upper level of said hearth.

5. An electric heating furnace comprising a heating hood, a furnace hearth having u Wardly sloping sides and extending a sub stantial distance into said hood and adapted to receive the furnace charge, and a resistance element arranged in the hood and extending from a point spaced a substantial distance above the upper hearth level to a point spaced a substantial distance below the upper level of the hearth.

6. An electric heating furnace comprising a furnace hood, a hearth extending a substantial distance into saidhood and adapted to receive the furnace charge, the sides of said hearth sloping upwardly away from the adjacent walls of the hood, a row of rib bon supports arranged on the inner walls of ,the hood and spaced a substantial distance and a resistance element arranged in said hood and extending below the top of the hearth, said hearth comprising a layer of heat insulating material having a centrally arranged core extending upwardly therefrom, fire-brick sides resting on the insulating layer and extending down the insulating core, said sides being spaced apart by the core, and a plurality of firebrick arranged upon the insulating core and connecting the sides of the hearth to form with the tops of the hearth sides a hearth top surface to support the furnace charge.

8. In an electric furnace, a furnace hood, a furnace hearth extending upwardly into said hood and adapted to support the furnace-charge, said hearth comprising a layer of heat insulating material having a censome trally arranged core extending upwardly therefrom, firebrick sides restin -on the ini sulating layer and extending sulating core, said sides bein e vs the in.-

err by the core, and a plurality of brick air--- ganged upon the insulating core and connecting the sides of the hearth to form with the tops of the hearth sides a hearth top surface to support the furnace In testimony whereof I afix n I GEORGE L Charge. m signature. 

